Asynchronous Transfer Mode (ATM) is a cell-based transport and switching technology. ATM provides high-capacity transmission of voice, data, and video within telecommunications and computing environments. ATM is a transport technology that formats all information content carried by the network into 53-byte cells. Since these cells are short in length and standard in size, they can be switched through network elements known as ATM switches with a little delay, using what is referred to as an ATM switch fabric. Since various types of traffic can be carried on the same network, bandwidth utilization can be very high. These characteristics make the network very flexible and cost effective. An ATM switch fabric operates to direct ATM cells from one interface to another. In this way the ATM switch fabric operates in response to dynamically changeable virtual connection information contained within the cell. ATM cells may be encapsulated and transmitted over SONET data frames, for example using STS-1 or STS-Nc, which is a concatenation of N STS-1 signals, or over SDH data frames using STM-1 or STM-N. STS-1 is a basic data stream in SONET, STM-1 is a basic data stream in SDH, wherein SONET (Synchronous Optical NETwork) and SDH (Synchronous Data Hierarchy) are synchronous hierarchies of data transmission, preferably via optical communication networks.
In many cases customers require support for both ATM switching and SONET/SDH switching in their communications systems. However, devices provided by vendors to support SONET have typically lacked the capability to also support ATM. In particular, typical existing ADMs (Add Drop Multiplexers) have supported only SONET/SDH ring networks, while existing ATM switches have generally supported only ATM networks.
Accordingly, if a customer has needed both SONET/SDH and ATM networks, they have necessarily had to purchase dedicated SONET/SDH equipment (ADMs), in addition to ATM switches. This is costly in terms of necessitating multiple devices. In addition, most customers cannot predict what their future communications requirements will be when they buy one piece of equipment. Because existing systems have been restricted to supporting only one of either SONET/SDH or ATM switching, they have not been flexible or scalable with regard to adding support for the other protocol. As a result of such inflexibility, changes in customer requirements may require the purchase of completely new devices to support a previously unsupported protocol. Accordingly, there was a need for a communication device which is capable of forming multiple configurations to support STM only, ATM only, or hybrid STM/ATM operation. Moreover, the device should be scalable such that additional functionality may be conveniently added as the needs of the customer change over time.
The above task was partially solved by providing a multi-service network node similar to that described in a European patent publication EP 1091529 A2.
EP 1091529 A2 describes a telecommunication network node capable of processing signals transmitted according to different protocols, namely a node with “multiprotocol” capability. The node is able to combine the homogeneous (or strictly shared out among the various types of traffic) payload of the frames coming into it. The node comprises means able to process the received frames and produce, according to the special needs, frames with homogeneous payloads and/or hybrid/multiprotocol payloads shared out in a flexible manner. The node avoids the need to construct different networks for each type of transmission (SHD, PDH, IP, ATM, Ethernet, . . . ). FIGS. 1a and 1b of the EP application illustrate a block-diagram of the node, comprising a number of input/output (I/O) blocks, a number of adaptation blocks and a switching fabric, being in this case an ATM/IP cell and packet switch. In the configuration described in EP 1091529 A2, all I/O ports of each specific I/O block are coupled/associated with a particular functional block responsible for adaptation of information received via this specific I/O block to the switching fabric of the node.
In practice, one I/O block comprising a number of I/O ports and its suitable adaptation function are implemented on one and the same printed card. The fact of predetermined interconnection between an I/O block and a particular adaptation function does not allow accessing this particular function from an I/O port not belonging to the mentioned I/O block, for example from any new location. Thereby, the above-described configuration with a pre-set design imposes problems when the network needs upgrading or modifying.
A similar problem exists in pure ATM or other switches where, due to the initial design, access to a particular adaptation function is limited by a number of I/O ports connected to the suitable functional adaptation block.
Another drawback of the solution proposed in EP 1091529 A2 is that the high order STM-N and the low order PDH data streams are treated in separate routes using separate matrices before applying thereof to adaptation functions. The matrices can be connected (say, for splitting a high order data stream into a number of low order data streams for further treatment) only via special adaptation functional blocks. Moreover, even if connected to one another, the low order matrix will be incapable of handling all high order data streams arriving to the high order matrix at a time (i.e., will be blocking), due to limitations which are intrinsic to the architecture of two-stage switching SDH/SONET equipment.
Another solution of a hybrid switching structure is WO 00/76156 A1, which describes architecture for a SONET network element, such as a hybrid STM/ATM add-drop multiplexer (ADM). The disclosed system includes an interconnection system for a network element, including a line unit LU (serving for aggregate line input/output), a switch fabric SF, and two or more service units SU serving for ADD-DROP input/outputs. The switching structure of WO 00/76156 A1 works as a typical ADM where two line (aggregate) links exist and all ADD-DROP traffic is cross-connected to both line links. In the WO 00/76156 A1, a network portion (LU units) and a client's add/drop portion (SU units) are not universal, i.e., cannot replace one another. The way of providing the ATM switching functionality in that solution is similar to the typical implementation of ATM switching equipment, where the I/O ports are permanently associated with specific service (adaptation) functions.
Also in the solution of WO 00/76156 A1, access to a particular adaptation function is limited by a number of I/O ports associated with a suitable functional adaptation block.